SYNTHESIS OF SPECIFICALLY DEOXYGENATED DISACCHARIDE DERIVATIVES OF THE SHIGELLA-DYSENTERIAE TYPE-1 O-ANTIGEN

The synthesis of methyl O-alpha-L-rhamnopyranosyl-(1 --> 2)-alpha-D-ga lactopyranosides specifically deoxygenated at position 2 (31), or 4 (2 1) of the rhamnopyranosyl residue was accomplished using methyl 3,4,6- tri-0-benzoyl-alpha-D-galactopyranoside (18) as the glycosyl acceptor. Phenyl thionocarbonate activation of the penta-O-benzoylated disaccha ride precursor followed by Barton reduction and Zemplen transesterific ation gave 31, while 21 was obtained via condensation of the deoxygena ted monosaccharide donor with 18, and subsequent debenzoylation of the product.